1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine or a laser printer or the like.
2. Related Background Art
In image forming apparatus such as copying machines or laser printers or the like, an image developed on a photosensitive member is transferred onto a recording material. Such image forming apparatus are provided with fixing devices for applying heat and pressure to the recording material on which the image has been transferred under specific fixing conditions so as to fix the image on the recording material.
Such conventional image forming apparatus are equipped with transmissive sensors for automatically detecting whether or not a recording material is an OHT sheet (i.e. an overhead transparent sheet). If the transmissive sensor detects that the recording material transmits light, it is determined that the recording material is an OHT sheet, while if the transmissive sensor detects that the recording material does not transmit light, it is determined that the recording material is a normal paper sheet. Thus, the fixing temperature or speed of the recording sheet under the fixing is set in accordance with a control based on the determination. Specifically, in the case of treating the OHT sheet, the image forming apparatus is so controlled as to increase the fixing temperature or to reduce the speed of the recording sheet passing through the fixing device, since it is necessary to stabilize and enhance the fixing of developer in order to maintain or enhance the transparency of the OHT sheet.
In general, the surfaces of OHT sheets for use in ink jet printers are being coated with a fixing agent for enhancing the fixing of the ink. In the past, if such an OHT sheet for use in ink jet printers is mistakenly fed to a copying machine or a laser printer or the like, the fixing agent on the OHP sheet for ink jet printers is melted by the heated fixing device to stick to the surface of a fixing roller. Consequently, the OHT sheet would entangle on the fixing roller to bring about not only jam in the sheet discharging but also, in the worst case, damage of a fixing roller guide or breaking of the fixing roller, which are worrying problems.
Even if the OHT sheet does not entangle on the fixing roller, there is a problem that a recording sheet that is subsequently fed would be contaminated with the fixing agent adhering on the fixing roller so that the image is deteriorated.
On the other hand, the transmissive sensors for discriminating the OHT sheet equipped in conventional image forming apparatus cannot detect whether or not an OHT sheet is coated with a fixing agent, though it can discriminate whether the recording material is a normal paper sheet or an OHT sheet. Therefore, if a user mistakenly feeds the image forming apparatus with an OHT sheet for ink jet printers, the printing is effected with a setting of fixing conditions according to a normal mode for OHT sheets, and the user would not notice that the recording material was mistakenly fed.
Furthermore, there has been another problem involving the fixing device. That is, if the user mistakenly sets a recording material having a thickness exceeding a prescribed regular thickness, the recording material cannot get into the fixing rollers, so that the recording material gets jammed so as to be corrugated, or that the thick recording material exerts an excessive pressure on a bearing of the fixing roller so as to break the fixing device.
The present invention has been made in view of the situations described above. An object of the invention is to prevent problems due to the feeding of an OHT sheet for ink jet, such as damaging of the fixing device or deterioration of the image, as well as damaging of the fixing device due to the feeding of a sheet with a thickness exceeding a regular thickness, and to give related information to the user, so as to provide an image forming apparatus and a control method thereof with which reliability and usability of the image forming apparatus can be enhanced.
According to the present invention, there is provided an image forming apparatus comprising, feeding means for feeding a recording material; image forming means for forming an image on the recording material fed by the feeding means; reading means capable of reading an image of an area including a portion of a surface of the recording material fed by the feeding means; determining means for determining whether or not the recording material is an irregular recording material, based on the image read by the reading means; and controlling means for stopping or suppressing, when it is determined by the determining means that the recording material is an irregular recording material, a specific operation of the apparatus.
According to the invention there is also provided a method of controlling an image forming apparatus in which a recording material is fed and an image is formed on the recording material that is being fed, comprising, a reading step of reading an image of an area including a portion of a surface of the recording material that is being fed; a determining step of determining whether or not the recording material is an irregular recording material, based on the image that has been read; and a controlling step of, when it is determined in the determining step that said recording material is an irregular recording material, stopping or suppressing a specific operation of the apparatus.
Other objects, features and advantages of the present invention will be readily apparent from the following description and the drawings.